Hypertension is a major problem in African-Americans but the contributing factors are poorly understood. This research proposal will compare vascular response and sympathetic regulation in African-Americans and Caucasians to allow examination of both factors and their interaction. These studies will attempt to physiologically localize the site of the attenuated response to isoproterenol in African-Americans that we have demonstrated and focus future molecular biology, mechanism-based techniques on these potential target sites. An understanding of the regulation of sympathetic activity by diurnal rhythm and stress will provide information about the role of these two mechanisms in the pathogenesis of hypertension and allow characterization of a prehypertensive state during which pharmacological intervention could arrest or retard the process.